In the past, as an apparatus for making a sheet (a surface sheet) adhere to the outer surface of a formed base material, a vacuum press lamination forming apparatus has been known (refer, for example, to Patent Document 1). However, in the vacuum press lamination forming apparatus, there are problems as described below.
Since a heating method is in-chamber radiation heating and elongation occurs due to softening of a sheet by the heating, it is necessary to suppress sag due to the stretching. Therefore, adjustment of vacuum pressure in upper and lower chambers is performed, thereby maintaining a horizontal state of the sheet. However, since it is difficult to confirm the exact amount of elongation of the sheet, a temperature distribution of the entire surface of the sheet becomes non-uniform and reliable forming and adhesion cannot be obtained, and thus stable quality is not obtained. Furthermore, position shift of a printed sheet with respect to the shape of a base material is generated.
Furthermore, in a case in which the inside of the lower chamber which becomes a base material side is depressurized after heating of the sheet, since according to the depressurization rate, the sheet moves toward the base material, thereby adhering to the base material, there is a concern that a pressing force of the sheet to the base material may become insufficient. For this reason, in a case in which a complex concavo-convex shape is present in the outer shape of the base material, if the pressing force of the sheet to the base material is insufficient, air stays between the concavo-convex portion and the sheet, thereby causing degrading of quality.
Furthermore, in thermoforming by the upper and lower chambers in the related art, since the volumes of the chambers are large, it takes time to perform depressurization and a cycle time becomes long, and thus the forming efficiency is reduced.
Therefore, as an apparatus capable of solving the problems of such a vacuum press lamination forming apparatus, there is proposed a thermo-former employing heat plate heating (refer to Patent Document 2).
The thermo-former is a thermo-former employing heat plate heating, which includes a bottom frame having a space capable of accommodating a base material, and a heat plate having a heating surface capable of coming into close contact with a frame upper edge portion of the bottom frame, and makes a sheet adhere to a shaped mold or the base material by disposing the sheet between the bottom frame and the heat plate and thermoforming the sheet, wherein the bottom frame is provided with depressurization means which can fix the sheet to the frame upper edge portion and depressurizes the space below the sheet, the heat plate is provided with depressurization means for suctioning the heating surface side, heating means for heating the heating surface, and means for opening the heating surface side to the atmosphere or pressurizing the heating surface side, and the thermo-former further includes suction and heating control means for performing suction and heating operations by the heat plate in a state in which the bottom frame and the heat plate come into close contact with each other with the sheet interposed therebetween, depressurization control means for performing a depressurization operation in the space below the sheet, and forming operation control means for making the suction and heating operations by the suction and heating control means and the depressurization operation by the depressurization control means be simultaneously performed, stopping the suction and heating operations after a predetermined time from the start of these operations, and opening the gap between the heat plate and the sheet to the atmosphere or pressurizing the gap between the heat plate and the sheet.
Then, according to the thermo-former, high-quality forming can be realized regardless of the shape of the base material, alignment of a printed sheet with respect to the shape of the base material can be favorably performed, and a cycle time required for forming is shortened, whereby higher efficiency of forming can be attained.